Simultaneous Moisture Content and Mass Flow Measurements in Wood Chip Flows Using Coupled Dielectric and Impact Sensors

Abstract

An 8-electrode capacitance tomography (ECT) sensor was built and used to measure moisture content (MC) and mass flow of pine chip flows. The device was capable of directly measuring total water quantity in a sample but was sensitive to both dry matter and moisture, and therefore required a second measurement of mass flow to calculate MC. Two means of calculating the mass flow were used: the first being an impact sensor to measure total mass flow, and the second a volumetric approach based on measuring total area occupied by wood in images generated using the capacitance sensor’s tomographic mode. Tests were made on 109 groups of wood chips ranging in moisture content from 14% to 120% (dry basis) and wet weight of 280 to 1100 g. Sixty groups were randomly selected as a calibration set, and the remaining were used for validation of the sensor’s performance. For the combined capacitance/force transducer system, root mean square errors of prediction (RMSEP) for wet mass flow and moisture content were 13.42% and 16.61%, respectively. RMSEP using the combined volumetric mass flow/capacitance sensor for dry mass flow and moisture content were 22.89% and 24.16%, respectively. Either of the approaches was concluded to be feasible for prediction of moisture content in pine chip flows, but combining the impact and capacitance sensors was easier to implement. In situations where flows could not be impeded, however, the tomographic approach would likely be more useful.

A comprehensive review on wood chip moisture content assessment and prediction

“…Dataset generation for MC prediction is highly time-dependent. The average number of data samples is low in the indirect methods reviewed in this study (e.g., in NIR Spectroscopy-based methods the data size ranged from 40 to 817 [17,24], and in the capacitance-based methods it ranged from 10 to 109 [31,42]). One of the reasons is that the data labeling depends on the oven drying process (gravimetric method), which is time-consuming.…”

“…Therefore, the recommended technique to use ECT for static MC prediction was to cover the sensing region with chips samples [15]. In another study, Pan et al [31] proposed a coupled dielectric and impact sensor-based method to simultaneously measure the MC and mass flow of moving wood chips. The authors concluded that the accuracy of the combined impact-capacitance sensor was similar to that of the stand-alone capacitance sensor.…”

“…The authors concluded that the accuracy of the combined impact-capacitance sensor was similar to that of the stand-alone capacitance sensor. Other limitations of the proposed ECT-based approach include the requirement of mass measurements of wood chips [15,31] and not being applicable in real-time [15,43]. Consequently, it is more practical to have a real-time ECT-based approach that does not require mass measurements.…”

Electrical Capacitance Characteristics of Wood Chips at Low Frequency Ranges: A Cheap Tool for Quality Assessment

“…They concluded that the system was sufficiently accurate in the MC range between 9% and 25% and that measurements at two frequencies helped to eliminate measurement errors. Pan et al [ 28 ] also tested coupled dielectric and impact sensor for simultaneous moisture content and mass flow of wood chips determination.…”

Wood Fuel Procurement to Bioenergy Facilities: Analysis of Moisture Content Variability and Optimal Sampling Strategy

“…In this frame, an effective quality control becomes a key factor for the supply chain [8]. Among all quality parameters, Moisture Content (MC) is considered the most relevant [9,10] as it may affect the whole supply chain up to energy conversion. The MC of woody fuels depends on several aspects such as species, inclusion of different tree parts (presence of leaves/needles) and season, among others [11,12].…”